The field of this invention generally includes instruments for monitoring the performance of bearings on rotating shafts and in particular systems for monitoring the operation of ball bearings in rotating machinery. The field of this invention also includes systems for measuring the angular position and size of unbalanced weight on electric motor and other machine rotors.
The prior art systems for monitoring the operation of ball bearings in rotating machinery use accelerometers or other vibration sensors mounted on the outside of the machine housings to detect the vibrations from the bearings. Vibrations which are produced by the rotor and transmitted to the machine housing through the bearing as well as vibrations produced within the bearings and vibrations produced in the housing of the machine are all detected by the vibration sensors. The frequency and amplitude characteristics of the vibrations produced within or transmitted through the ball bearings are considerably changed by the time the vibrations reach the sensors mounted on the outside of the machine housing. These changes result from the fact that the transmission path travelled by these vibrations through the machine housing has its own resonance, attenuation and phase shift characteristics which are imposed upon the vibration signals from the bearings. These transmission characteristics between the bearings and the sensors mounted on the outside of the machine housing may vary widely as the sensors are moved from one place to another. Therefore, the signals produced by these vibration sensors are difficult to interpret. One common practice is to record baseline data on the frequency spectrum of the vibrations produced by each type of machine while in operation. With a given ball bearing in the machine and with the machine operating at a given speed, certain of the peaks in the frequency spectrum are identified as being produced within the bearings. When one of these bearing related peaks in the vibration frequency spectrum increases in amplitude, an oncoming bearing failure is indicated. Interpreting vibration data in this manner tends to be very difficult since the vibration frequency which indicates bearing failure will depend upon the location of the vibration sensor, the type of bearing, the size and shape of the machine housing, and on the clearances between the bearing and its housing. Any variable which may change the transmission path of the vibrations as they travel from the bearing to the vibration sensor will effect the baseline vibration data and make this data more difficult to interpret.
When the rotor of a machine is not perfectly balanced, it will produce vibrations at its frequency of rotation. These vibrations will be transmitted through the bearings and the machine housing and may be detected by the same vibration sensors as are used to monitor the bearing operation. The machine's rotor may be balanced by attempting to add or subtract weight from the rotor in such a way as to minimize this signal. However, the vibration waves undergo varying amounts of attenuation and phase shift as they travel from the out of balance rotor through the bearing and machine housing to the vibration sensors. The size of these phase shifts depend upon the size and shape of the machine housing as well as the location of the sensors on the housings. Therefore it is difficult to determine the angular position on the rotor from which weight should be added or subtracted to balance the rotor.
The present inventor has found that these problems in the prior art could be solved if the vibrations were measured at the ball bearings themselves and not at some location remote from the ball bearings. Accordingly, it is an objective of this invention to measure vibration directly on the surfaces of ball bearings before the vibration signals are distorted by travelling through the machine housing and other structures. The inventor found that if vibrations are measured directly from the surfaces of a rotating ball bearing, it is easier to determine the sources or causes of the individual components of the vibration signals. Accordingly, another objective of this invention is to simplify the analysis required to interpret the vibration signals received from ball bearings. A third objective of the invention is to provide a system which can monitor from a central location the operation of ball bearings on several widely dispersed pieces of machinery. A fourth objective of this invention is to provide a simplified but accurate method of determining the angular position of unbalanced weight on rotors supported by ball bearings.